Her vision of a nationwide movement for change restoring family values, effort, earnestness and excellence brought to the fore the question of the gang culture, of which headteacher Mr Lawrence’s killer, Learco Chindamo, was a product.

There is a widespread acknowledgement that many young people are affected by a culture of violence, and that schools have to cope with it.

Disturbing evidence of its widespread nature emerged earlier this year, when researchers at the University of Exeter found almost a third of 14 and 15-year-old boys sometimes carried a weapon for protection; one in five sometimes carried a blade.

The university’s Schools Health Education Unit director, John Balding, said gang culture was likely to have an effect. He said: “I’m sure personally that if you’re in a gang you carry a weapon because everybody carries one; it’s very likely that if someone carries, they know other people who do.”

The unit’s report, Cash and Carry, based on responses from more than 5, 000 Year 10 pupils, also found worrying parallels between drugs and the weapons culture.

Research by Professor Sir Michael Rutter and Professor David Smith last year painted an equally gloomy picture, recording a dramatic rise in criminality, as well as depression, suicide and alcoholism, among young people since the Second World War.

John Sutton, general secretary of the Secondary Heads Association, acknowledged that a gang and weapons culture was prevalent in Britain’s deprived urban areas.

He said teachers largely succeeded in keeping violence outside the school gates, but he warned they cannot change what happens in society at large.

“The average pupil spends only 20 per cent of his or her life inside school, ” he said.“You would find people working in very disadvantaged areas would say development is the key to the issue.”

David Hart, general secretary of the National Association of Head Teachers, warned: “We have an increasing sub-culture, which is worrying, and we have an increasing underclass which is out of control. Schools obviously suffer from this growing underclass.

“Many children are almost out of reach, many of them come from poor or disadvantaged backgrounds or from families with a record of criminality. ” The Exeter research supports the view that teachers are able to control events within the classroom - few teenagers admitted carrying weapons to school.

But the study’s scope - it covered Cornwall, Cumbria and Devon, as well as urban areas such as the West Midlands and Teesside - suggested there was more to the weapons culture than simple urban deprivation.

Popular opinion often sees the influence of film and television as a key factor contributing to a culture of violence in society.

But research by Professor Tony Charlton, professor of behaviour studies at the Cheltenham and Gloucester College of Higher Education, casts doubt on that view.

He has spent five years studying the effects of television on the people of the tiny island of St Helena in the mid-Atlantic.

Television, in the form of the Cable News Network, only came to the isolated community 18 months ago, providing Professor Charlton and his team the ideal opportunity to study the effects of televised violence on the island’s schoolchildren.

He has found no deterioration in children’s behaviour, and has even noticed some beneficial effects.

He said: “We looked at children’s behaviour before and after television arrived. The current state of information is there is no evidence to show 18 months after the arrival of broadcast television that behaviour has deteriorated.”

But his work supports the view that the family can keep the culture of violence at bay. Professor Charlton pointed to the strong family ties, and the fact that children watched television with their relatives as a significant factor helping St Helena’s children to cope with the often violent images of television news.

Peter Wilson, director of the children’s mental health charity Young Minds, said that violence on television and in films did affect children.

But he said the influence of family breakdown, economic distress and insecurity were important parts of the jigsaw.

“There is a significant number of children living their lives at the moment in families which are not secure or in which there’s a lot of violence going on,” he said.

“How we support families to live better lives in better circumstances where they can bring their kids up with less resentment and less hurt than in the past is a major practical issue.

“We have to help all children to be like the 80 per cent who never have problems.”